Graphics display systems in devices such as mobile telephones typically employ a graphics controller, which acts as an interface between one or more sources of image data and a graphics display device such as an liquid crystal display (“LCD”) panel or panels. In a mobile telephone, the sources of image data are typically a camera and a host such as a CPU. The host and camera transmit image data to the graphics controller for ultimate display on the display device. The host also transmits control data to both the graphics controller and the camera to control the operation of these devices.
Graphics controllers typically provide various processing options for processing image data received from the host and camera. For example, the graphics controller may compress or decompress, e.g., JPEG encode or decode, incoming or outgoing image data, crop the image data, resize the image data, scale the image data, and color convert the image data according to one of a number of alternative color conversion schemes. All these image processing functions provided by the graphics controller are responsive to and may be directed by control data provided by the host.
The host also transmits control data for controlling the camera to the graphics controller, the graphics controller in turn programming the camera to send one or more frames of image data acquired by the camera to the graphics controller. Where, as is most common, the graphics controller is a separate integrated circuit, and the graphics controller, the host, and the camera are all remote from one another, instructions are provided to the camera, and image data from the camera are provided to the graphics controller for manipulation and ultimate display, through a camera interface in the graphics controller. Typically, the “capture” of image data obtained from a camera includes storing the data in a frame buffer in the graphics controller. The data are subsequently fetched from the frame buffer and provided to a display device interface of the graphics controller for transmission over a bus to the graphics display device.
Data storage and retrieval consume power as well as processing overhead, and it is always desirable to minimize such processing. The inventors have recognized that, in order to minimize processing overhead, it would be desirable if the graphics controller only processed the image data received from the host and camera when the subject being imaged moves. Accordingly, there is a need for a graphics controller providing an ordinary, capture mode for processing data received from an external camera and a low-power, monitoring mode of operation that can be used in circumstances in which it is not necessary to capture or otherwise fully process the data.